U.S. government subcontractor Alan P. Gross, serving a 15-year prison sentence in Havana, went on a hunger strike after learning that Washington had financed a semi-clandestine Twitter-like system for Cubans, his U.S. lawyer said Tuesday.

Attorney Scott Gilbert said Gross told him in a phone conversation Tuesday afternoon that he had not eaten since Thursday but is drinking water and has lost about 10 pounds, on top of the 100 pounds he lost since his arrest in late 2009.

“When I asked him how long he planned to continue the hunger strike,” said Gilbert, “he said, ‘as long as it takes.’ ”

Gross said the “final straw” that prompted his hunger strike came when he learned on Thursday that the U.S. Agency for International Development (USAID) had launched the controversial Twitter-like platform after his arrest, Gilbert said.

Gilbert had criticized USAID earlier Tuesday for launching the semi-secret Zunzuneo platform in 2010, saying that it represented an additional risk for the 64-year-old USAID subcontractor from Potomac, Md. The program was first disclosed by The Associated Press.

The Gross family was told “that there were no further covert missions in Cuba. We’ve been assured that nothing like this was going on. Either we were lied to or the people who were speaking to us were being deceived,” he told El Nuevo Herald.

USAID and the White House have said that the Zunzuneo program was not “covert,” but required discretion because Cuba has outlawed cooperation with all USAID programs as “subversive.” USAID says the programs only promote democracy and civil society.

Gross’ continued detention in Havana has become one of the key roadblocks to the Obama administration’s efforts to improve relations with the communist-ruled island.

A statement issued early Tuesday by Gross family spokesperson Jill Zuckman quoted Gross as announcing the hunger strike but making no mention of the Zunzuneo program.

“I began a fast on April 3 in protest of the treatment to which I am subjected by the governments of Cuba and the United States,” he was quoted as saying. “I am fasting to object to mistruths, deceptions, and inaction by both governments, not only regarding their shared responsibility for my arbitrary detention, but also because of the lack of any reasonable or valid effort to resolve this shameful ordeal.”

That statement also quoted Gross’ wife, Judy Gross, as saying that she is “worried sick about Alan’s health, and I don't think he can survive much more of this.”

Zuckman told El Nuevo Herald that Gross had declared his hunger strike because “he has lost hope” that Washington and Havana will be able to negotiate his freedom anytime soon.

“On the fourth anniversary of his arrest in December, Alan felt gratified by the support he was receiving and felt there was some hope that the United States and Cuba would find a path forward so that he could go home,” Zuckman said.

“Four months later he has lost hope and feels he has no other way of getting people to listen to him and to resolve his situation,” she added. Zunzuneo “had something to do with it [the hunger strike], but the bigger issue is Alan is losing hope.”

Gross was arrested Dec. 3, 2009, and accused of delivering sophisticated communications equipment financed by USAID to Cuban Jews so they could bypass Cuban government controls on access to the Internet.

Havana has offered to free Gross in exchange for three Cuban spies serving long sentences in U.S. prisons for conspiracy to spy on U.S. military and exile targets. Two others completed their sentences and returned to Havana.

Obama administration officials have repeatedly and flatly said there will be no swap, especially because Gross is not a spy and one of the jailed Cubans is serving a life sentence for his role in Cuba’s killing of four Brothers to the Rescue pilots in 1996.

Jose Miguel Insulza, secretary general of the Organization of American States, told the Miami Herald on Tuesday that he believes the hunger strike is a bad idea for a man in ill health like Gross, but hopes that it will help to get him out of Cuba.

“If it’s possible to open some kind of negotiations, it would not only be good for the people involved. It would also be good for a better climate in U.S.-Cuba relations, which are so important,” Insulza said after speaking at the Palm Beach Strategic Forum.

USAID Administrator Rajiv Shah, meanwhile, testified at a Senate hearing Tuesday that the agency was aware that Gross ran the risk of getting arrested in Cuba because the island’s communist government had outlawed the pro-democracy programs

But “the detention of Gross is wrong, and the responsibility rests with the Cuban authorities,” Shah told the hearing, which also touched on the controversy surrounding the Zunzuneo program.